Faint but regular clicks/pops in MBP (Quad Core 2011, 2.0) headphone output

Question

I've seen some scattered posts about this. In my case it's definitely not the motion sensor as it happens if the computer is totally still. I can hear it with the audio turned all the way down and no applications running. It happens every 30 seconds or so-- there's a sharp click followed by a faint electrostatic hum for maybe a second or so. I'm sending it in to have it evaluated. I noticed it immediately upon setting it up for the first time. I reinstalled Snow Leopard and reset the PRAM, neither of which helped. If I install one of my audio interfaces (Saffire DSP Pro or M-Audio FW 410 but still using the Core Audio driver) it does not pass through the firewire to the device. Anyone else having this issue? My old MBP (first gen 2.0 GHz Intel w/CoreDuo) does not display this symptom.

Answer 1

Took my MBP into the Genius Bar and got a replacement and the new machine (out of the box and running Lion, whereas the first one was among the last to ship with SL) behaves identically. I'm wondering if this is a feature, as I'm just now realizing that what I'm hearing may be the audio driver or headphone jack periodically switching on and off. I can make the click happen by doing anything that calls on the core audio driver. This may be clicking on a song in iTunes or even switching between tabs in Firefox if one of them has a lot of streaming content. The click is followed by a little bit of hiss; then, if I do nothing, there's another click maybe 30 seconds later and the headphone port goes completely silent. The 'hiss' is, I suspect, just the normal background noise on the output. When there's actual sound being output (a song, flash video, QT playback etc) there are no clicks or other artifacts. Likewise if I listen to the headphone output for 10-15 mins while doing nothing else (big fun, let me tell you).
If that's what's happening it's an annoyance but not the end of the world. I can't think of a good reason why it should behave like this (i.e. to save power or otherwise redirect resources) and it reeks of crappy hardware or coding, but if it's not affecting the actual headphone or firewire audio output when sound is happening I can live with it.
I could be totally off the mark and for all I know tomorrow it could be doing the above and clicking randomly during audio playback. Curious to know if anyone else who is having this symptom sees the same pattern.
Cheers.